This invention relates to chelators that form a mixture enriched for a single stereoisomeric species upon coordination to a metal center.
The current interest in the radiolabeling of biologically important molecules (proteins, antibodies, and peptides) with 99mTc stems from the desire to develop a target specific diagnostic radiopharmaceutical.1-10 The advantages of using 99mTc in diagnostic nuclear medicine are well known11-15 and a number of techniques have been developed for the 99mTc labeling of biologically important molecules.16-20 One obvious approach is to coordinate a 99mTc metal directly with the targeting molecule. This approach is known as the direct labeling method and it involves the use of a reducing agent to convert disulfide linkages into free thiolates, which then bind to the 99mTc metal. A major disadvantage of this method is the lack of control over the coordination of the 99mTc metal and the stability of the resulting metal complex. In addition, the lack of suitable or accessible coordination sites in some proteins and peptides exclude direct labeling as a viable technique. Two common alternatives to direct labeling are the final step labeling method and the pre-formed chelate approach. Both techniques involve the use of a bifunctional chelator, which provides the site of 99mTc coordination. The difference between the two approaches lies in the order in which the 99mTc complex is formed. In the final step labeling method, complexation occurs after the chelator has been attached onto the targeting molecule. With the pre-formed chelate method, the 99mTc complex is initially prepared and purified before being attached to the targeting molecule. In both techniques, the bifunctional chelator must coordinate to 99mTc to form a complex that is stable in vivo and the chelator must have an active moiety that can react with a functional group on the targeting molecule.
A number of bifunctional chelators have been used in the labeling of proteins, peptides and monoclonal antibodies.2,9,10,17,21-28 Depending on the chelator, the labeling of biologically important molecules with bifunctional chelators often results in the formation of multiple species and/or isomeric complexes. An example is the 99mTc labeling of molecules using the hydrazinonicotinamide (HYNIC) system. Since the HYNIC group can only occupy one or two sites of Tc coordination, co-ligand are required to complete the coordination sites. Glucoheptonate29-30, tris(hydroxymethyl)methylglycine (tricine)25, ethylenediamine-N, Nxe2x80x2-diacetic acid (EDDA)9, water soluble phosphines25 [trisodium triphenylphosphine-3,3xe2x80x2,3xe2x80x3-trisulfonate (TPPTS); disodium triphenylphosphine-3,3xe2x80x2disulfonate (TPPDS); and sodium triphenylphosphine-3-monosulfonate (TPPMS)] and polyamino polycarboxylates9 have all been used as co-ligand in the HYNIC system. It has been clearly shown the Tc-99m labeling of molecules via the HYNIC/co-ligand system produces multiple species, which is due to the different coordination modalities of the hydrazine moiety and the co-ligands. The number of species, the type, the stability and the properties of the species vary greatly from one co-ligand to another. In the labeling of chemotatic peptide using the HYNIC system, the nature of the co-ligand also greatly affects the biodistribution of the labeled peptide.31 
Another example of a bifunctional chelator producing multiple species is dithiosemicarbazone (DTS) system. It has been shown that the DTS bifunctional chelator produces at least four complexes with technetium.32 Two of the complexes are known to be charged; hence they have different biodistribution from the uncharged species.
As in the development of a pharmaceutical based on organic molecules, the stereochemistry or isomerism of a metal complex is also very important in the development of a radiopharmaceutical or metallodrug. It is well known that isomers can often have different lipophilicities, biodistribution and biological activities. An example of this is the 99mTc complex of 3,6,6,9-tetramethyl-4,8-diazaundecane-2,10-dione dioxime (99mTc-d,1-HMPAO or Ceretec), which is a cerebral perfusion imaging agent.14,33-35 Though 99mTc-d,1-HMPAO is active, it has been shown that the meso analogs of the 99mTc HM-PAO14,36 complex and the 99mTc complex of 3,3,9,9-tetramethyl-4,8-diazaundecane-2,10-dione dioxime14,37 (PnAO) does not possess the properties necessary for use as a cerebral perfusion imaging agent.
A type of Tc and Re coordination modality common in Tc and Re radiopharmaceuticals is the coordination of a tetradentate N4xe2x88x92xSx chelator to a metal oxo moiety to form a square pyramidal or octahedral metal oxo complex. A host of bifunctional chelators have been developed based on the tetradentate N4xe2x88x92xSx coordination motif. Examples include N4 propylene amine oxime38, N3S triamide thiols9, 39-43, N2S2 diamide dithiols9, 44-46, N2S2 monoamide monoaminedithiols47-49 and N2S2 diamine dithiols50-55. Functionalization of the chelator backbone enable these chelators to be attached to biologically interesting molecules. The labeling of these bifinctional chelators with TcO3+ or ReO3+ often produce isomers or epimers.39-43, 46-55 The isomers or epimers (syn and anti) arise from the configuration of the metal oxo group relative to the functional group on the chelator backbone. It has been clearly shown that the biodistribution and biological activity of the syn and anti isomers are often different.39-43, 46, 56 The Tc complex of mercaptoacetylglycylglycylglycine (MAG3), a renal imaging agent, exists in the syn and anti isomers. The biological activities of the syn and anti isomers are known to be different.39,40 The syn and anti isomers of the Tc complex of 2,3-bis(mercaptoacetamide)propanoate (map) was also shown to have different biological activity.46 It was reported that in humans, 58% of the syn isomers was excreted at 30 minutes as compared to only 19% of the anti isomer. Another example of the isomers exhibiting a difference in biological behaviour is the 99mTc labeled diamino dithiol piperidine conjugate, which were investigated as a brain perfusion imaging agents. It was shown that the two isomeric complexes exhibit widely disparate brain uptake.55 At 2 minute post-administration in rats, uptake of the anti isomer in the brain was 1.08% dose/g, while the uptake of the syn isomer was 2.34% dose/g. The brain/blood ratio at 2 minute post-administration was 2.09 for the anti isomer and 5.91 for the syn isomer.
The peptide dimethylglycine-serine-cysteine-glycine is a bifunctional chelator that can be use to label biologically important molecules.61,62 It has been shown that dimethylglycine-serine-cysteine-glycine coordinates to TcO3+ and ReO3+ via a monoamine diamide monothiol coordination modality.61 The resulting Tc and Re complexes exist as two isomers; the serine CH2OH side chain is in the syn and anti conformations with respect to the metal oxo bond. The presence of the syn and anti isomers are very evident from the NMR spectral data. In the 1H NMR spectrum of the Re complex, there were two pairs of singlets associated with the nonequivalent methyl groups in the dimethylglycine residue. Each pair of singlets corresponded to either the syn or anti isomers. The 1H and 13C NMR spectral data for the Re oxo complex of dimethylglycine-sercine-cysteine-glycine-NH2 (RP294) were obtained. The presence of the two isomers are clearly evident from the NMR data. In the coordination of dimethylglycine-isoleucine-cysteine-glycine (RP349) to ReO3+, two isomers (syn and anti) were also observed. The 99mTc labeling of RP294 and RP349 produced syn and anti isomers; two peaks were observed in the HPLC using the radiometric detector. The 99mTc labeling of biotin with dimethylglycine-lysine-cysteine-NH2 (RP332) also produced syn and anti isomers; two peaks were observed in the HPLC. These results are consistent with the coordination of other tetradentate N4xe2x88x92xSx chelators to TcO3+ and ReO3+.9,39-55 
The labeling of biologically important molecules via a bifinctional chelator can result in the formation of isomers or multiple species, which can have significant impact on the biological properties of the radiopharmaceutical. For receptor-based radiopharmaceuticals, the target uptake is largely dependent on the receptor binding affinity of the targeting molecule and the blood clearance of the labeled molecule, which is determined by the physical properties of both the targeting molecule and the metal chelate. Hence, the presence of isomers for the metal chelate can have significant impact on the radiopharmaceutical. Therefore, in the development of a radiopharmaceutical or metallodrug, it is necessary to separate the isomers and evaluate the biological activities of each individual isomer. It would therefore be desirable to develop chelators that predominately form only a single stereoisomeric species upon coordination to a metal center.
Chelators and chelator-targeting molecule conjugates are provided that form a mixture enriched for a single stereoisomeric species upon coordination to a metal center.
According to an aspect of the invention, there is provided a chirally pure compound of the formula I: 
wherein
R1 is a linear or branched, saturated or unsaturated C1-4alkyl chain that is optionally interrupted by one or two heteroatoms selected from N, O and S; and is optionally substituted by one or more substituents selected from halogen, hydroxyl, amino, carboxyl, C1-4alkyl, aryl and C(O)R10;
R2 is H or a substituent defined by R1;
R1 and R2 may together form a 5- to 8-membered saturated or unsaturated heterocyclic ring optionally substituted by one or more substituents selected from halogen, hydroxyl, amino, carboxyl, oxo, C1-4alkyl, aryl and C(O)R10;
R3, R4 and R5 are selected independently from H; carboxyl; C1-4alkyl; C1-4alkyl substituted with a substituent selected from hydroxyl, amino, sulfhydryl, halogen, carboxyl, C1-4alkoxycarbonyl and aminocarbonyl; an alpha carbon side chain of a D- or L-amino acid other than proline; and C(O)R10;
R6 is an optionally subsituted 3- to 6-membered heterocylic or carbocylic ring;
or R6 is 
wherein R11, R12 and R13 are independently selected from H, linear or branched, saturated or unsaturated C1-6alkyl chain that is optionally interrupted by one or two heteroatoms selected from N, O and S; and is optionally substituted by one or more substituents; alkoxycarbonyl, aminocarbonyl, alkoxy, an optionally subsituted 3- to 6-membered heterocylic or carbocylic ring; with the proviso that a least one of R11, R12 and R13 is not H;
or R6 is 
wherein R14 and R15 are independently selected from H, linear or branched, saturated or unsaturated C1-6alkyl chain that is optionally interrupted by one or two heteroatoms selected from N, O and S; and is optionally substituted by one or more substituents; alkoxycarbonyl, aminocarbonyl, alkoxy, an optionally subsituted 3- to 6-membered heterocylic or carbocylic ring; with the proviso that a least one of R14 and R15 is not H;
or R6 is 
wherein X is selected from O or S and R16 is selected from linear or branched, saturated or unsaturated C1-6alkyl chain that is optionally interrupted by one or two heteroatoms selected from N, O and S; and is optionally substituted by one or more substituents; alkoxycarbonyl, aminocarbonyl, alkoxy, and an optionally subsituted 3- to 6-membered heterocylic or carbocylic ring;
R7 and R8 are selected independently from H; carboxyl; amino; C1-4alkyl; C1-4alkyl substituted by a substituent selected from hydroxyl, carboxyl and amino; and C(O)R10;
R9 is selected from H and a sulfur protecting group; and
R10 is selected from hydroxyl, alkoxy, an amino acid residue, a linking group and a targeting molecule.
According to another aspect of the invention, there is provided a chirally pure compound of the formula II: 
wherein
Ra is selected from H and a sulfur protecting group;
Rb, Rc Rd, Rf and Rg are selected independently from H; carboxyl; C1-4alkyl; C1-4alkyl substituted with a substituent selected from hydroxyl, amino, sulfhydryl, halogen, carboxyl, C1-4alkoxycarbonyl and aminocarbonyl; an alpha carbon side chain of a D- or L-amino acid other than proline; and C(O)Rh;
Re is an optionally subsituted 3- to 6-membered heterocylic or carbocylic ring;
or Re is 
wherein Ri, Rj and Rk are independently selected from H, linear or branched, saturated or unsaturated C1-6alkyl chain that is optionally interrupted by one or two heteroatoms selected from N, O and S; and is optionally substituted by one or more substituents; alkoxycarbonyl, aminocarbonyl, alkoxy, an optionally subsituted 3- to 6-membered heterocylic or carbocylic ring; with the proviso that a least one of Ri, Rj and Rk is not H;
or Re is 
wherein Rl and Rm are independently selected from H, linear or branched, saturated or unsaturated C1-6alkyl chain that is optionally interrupted by one or two heteroatoms selected from N, O and S; and is optionally substituted by one or more substituents; alkoxycarbonyl, aminocarbonyl, alkoxy, an optionally subsituted 3- to 6-membered heterocylic or carbocylic ring; with the proviso that a least one of Rl and Rm is not H;
or Re is 
wherein X is selected from O or S and Rn is selected from linear or branched, saturated or unsaturated C1-6-alkyl chain that is optionally interrupted by one or two heteroatoms selected from N, O and S; and is optionally substituted by one or more substituents; alkoxycarbonyl, aminocarbonyl, alkoxy, and an optionally subsituted 3- to 6-membered heterocylic or carbocylic ring; and
Rh is selected from hydroxyl, alkoxy, an amino acid residue, a linking group and a targeting molecule.
According to another aspect of the invention, the chelator-targeting molecule conjugates are provided in combination with a diagnostically useful metal or an oxide or nitride thereof.
According to another aspect of the present invention, there is provided a method of imaging a site of diagnostic interest, comprising the step of administering a diagnostically effective amount of a composition comprising a chelator-targeting molecule conjugate which is complexed to a diagnostically useful metal or an oxide or nitride thereof.
In the coordination of dimethylglycine-t-butylglycine-cysteine-glycine [SEQ ID NO:1] to TcO3+ and ReO3+, an single isomer was observed. A single pair of singlets associated with the methyl groups in the dimethylglycine residue was observed. The 1H and 13C NMR spectral data for the Re oxo complex of dimethylglycine-L-t-butylglycine-L-cysteine-glycine [SEQ ID NO:2]. The 99mTc labeling of dimethylglycine-L-t-butylglycine-L-cysteine-glycine [SEQ ID NO:2] (RP455) and of dimethylglycine-D-t-butylglycine-L-cysteine-glycine [SEQ ID NO:3] (RP505) produced a single peak as observed in the HPLC using the radiometric detector. This was an unexpected result and is in contrast with what is observed in the Tc and Re oxo complexes of other tetradentate N4xe2x88x92xSx chelators,9, 39-55 which exist as the syn and anti isomers.
The presence of a sterically bulky group in the side chain of the peptidic chelator cause the formation of a single isomeric metal complex. In the cases of dimethylglycine-lysine-cysteine and dimethylglycine-serine-cysteine-glycine, [SEQ ID NO:6] there are insufficient bulk to cause one isomer to be preferred over another; hence the ratio of the syn and anti isomers is approximately 1:1. In the case of dimethylglycine-isoleucine-cysteine, a more sterically bulky CH(CH3)xe2x80x94CH2xe2x80x94CH3 group was introduced into the peptidic backbone. This additional bulk caused the ratio of the syn and anti isomers to be 3:1; hence, one isomer was more favored over the other. In the case of dimethylglycine-t-butylglycine-cysteine-glycine, [SEQ ID NO:1] the incorporation of the C(CH3)3 group introduced sufficient bulk into the peptide to cause one of the isomer to be completely favored over the other; hence, a single isomeric metal complex was observed.
Molecular modeling using Quanta Charm of the Re complexes of these peptides is in agreement with the experimental results. Molecular modeling of the Re complex of dimethyglycine-L-serine-L-cysteine-glycine [SEQ ID NO:4] show the two isomers possessing thermodynamic potential energies of xe2x88x9267.02 and xe2x88x9268.37 kcal/mole. There is only a small difference in the energy of the two isomers. There is no preferred isomer for the Re complex and both the syn and anti isomers are observed at an approximate ratio of 1:1. Molecular modeling of the Re complex of dimethylglycine-lysine-cysteine shows a difference between in the thermodynamic potential energies of the two isomers to be approximately 1 kcal/mole. There is only again a small difference in the energy of the two isomers; hence both the syn and anti isomers should be observed.
In the case of dimethylglycine-L-isoleucine-L-cysteine-glycine, [SEQ ID NO:5] a more bulky side chain is incorporated into the peptidic backbone. Molecular modeling of the Re complex of the dimethylglycine-isoleucine-cysteine-glycine [SEQ ID NO:12] show one of the isomer having a potential energy that is approximately 3 kcal/mole lower than the energy of the other isomer. There is a now a greater difference in the energies and there is a slight preference for one isomer over the other. Hence, the ratio of the two isomers is 3:1.
In the case of dimethylglycine-L-t-butylglycine-L-cysteine-glycine, [SEQ ID NO:2] molecular modeling of the Re complex shows the difference in the potential energies of the two isomers to be approximately 6.5 kcal/mole. With the Re complex of dimethylglycine-D-t-butylglycine-L-cysteine-glycine, [SEQ ID NO:3] the difference in the energies of the two isomers is about 8.5 kcal/mole. One isomer is significantly preferred over the other; hence, only a single isomer is observed for the Re and Tc complexes. Molecular modeling of the Re complex of mercaptoacetyl-t-butylglycine-glycine-glycine shows that the syn and anti isomers of the complex with a energy difference of 7.4. The metal complexes of mercaptoacetyl-t-butylglycine-glycine-glycine preferred one isomer over the other and should exist as a single isomer.
Artificial amino acids with bulky side chains can be prepared according to known literature methods.63-67 For example, both L- and D-amino acid derivatives can be prepared starting directly from the commercially available L- or D-serine, respectively.67 Using this method, alkyl, phenyl and other bulky groups can be incorporated into serine to produce xcex2-hydroxy-xcex1-amino acids.67 Hence, artificial amino acids with bulky side chains can be incorporated into peptidic chelators, which would produce a single species and an single isomeric metal complex.
The advantage of having a bifunctional chelator that forms a single isomeric metal complex is that in the labeling of biologically important molecule, there is only a single radiolabeled species. Hence, there is no need to isolate and evaluate the biological activity and toxicity of multiple compounds. It is also easier to formulate a radiopharmaceutical kit that consistently produces a single radiolabeled compound than one that produces a series of radiolabeled compounds. In the labeling of a biologically important molecule with a chelator that results in multiple species, there is a necessity to formulate the kit such that the labeling consistently produce the same set of compounds in the same ratio. This is eliminated with the use of a chelator that produces a single metal complex. Quality control of a radiopharmaceutical is also simplified by the use of a chelator that result in a single species as it is much easier to develop a quality control protocol that identifies a single well characterized compound than one that have to identify the presence and quantity of multiple compounds.
An addition benefit from the incorporation of different side chain groups into the peptidic chelator backbone to cause a single isomer is that the lipophilicity of the resulting metal complexes is altered by the addition of the different groups. The log D of the 99mTc complex of dimethylglycine-t-butylglycine-cysteine-glycine [SEQ ID NO:1] is xe2x88x921.3, compared to xe2x88x922.3 for the 99mTc complex of dimethylglycine-serine-cysteine-glycine.[SEQ ID NO:6]
The terms defining the variables R1-R10, Ra-Rn and X as used hereinabove in formula (I) have the following meanings:
xe2x80x9calkylxe2x80x9d refers to a straight or branched C1-C8 chain and includes lower C1-C4 alkyl;
xe2x80x9calkoxyxe2x80x9d refers to straight or branched C1-C8 alkoxy and includes lower C1-C4 alkoxy;
xe2x80x9cthiolxe2x80x9d refers to a sulfhydryl group that may be substituted with an alkyl group to form a thioether;
xe2x80x9csulfur protecting groupxe2x80x9d refers to a chemical group that is bonded to a sulfur atom and inhibits oxidation of sulfur and includes groups that are cleaved upon chelation of the metal. Suitable sulfur protecting groups include known alkyl, aryl, acyl, alkanoyl, aryloyl, mercaptoacyl and organothio groups.
xe2x80x9cLinking groupxe2x80x9d refers to a chemical group that serves to couple the targeting molecule to the chelator while not adversely affecting either the targetting function of the peptide or the metal binding function of the chelator. Suitable linking groups include alkyl chains; alkyl chains optionally substituted with one or more substituents and in which one or more carbon atoms are optionally replaced with nitrogen, oxygen or sulfur atoms. Other suitable linking groups include those having the formula A1xe2x80x94A2xe2x80x94A3 wherein A1 and A3 are independently selected from N, O and S; and A2 includes alkyl optionally substituted with one or more substituents and in which one or more carbon atoms are optionally replaced with nitrogen, oxygen or sulfur atoms; aryl optionally substituted with one or more substituents; and heteroaryl optionally substituted with one or more substituents. Still other suitable lining groups include amino acids and amino acid chains functionalized with one or more reactive groups for coupling to the glycopeptide and/or chelator. In one embodiment, the linking group is a peptide of 1 to 5 amino acids and includes, for example, chains of 1 or more synthetic amino acid residues such as xcex2-Alanine residues. In another embodiment, the linking group is NH-alkyl-NH.
xe2x80x9cTargeting moleculexe2x80x9d refers to a molecule that can selectively deliver a chelated radionuclide or MRI contrasting agent to a desired location in a mammal. Preferred targeting molecules selectively target cellular receptors, transport systems, enzymes, glycoproteins and processes such as fluid pooling. Examples of targeting molecules suitable for coupling to the chelator include, but are not limited to, steroids, proteins, peptides, antibodies, nucleotides and saccharides. Preferred targeting molecules include proteins and peptides, particularly those capable of binding with specificity to cell surface receptors characteristic of a particular pathology. For instance, disease states associated with over-expression of particular protein receptors can be imaged by labeling that protein or a receptor binding fragment thereof coupled to a chelator of invention. Most preferably targeting molecules are peptides capable of specifically binding to target sites and have three or more amino acid residues. The targeting moiety can be synthesised either on a solid support or in solution and is coupled to the next portion of the chelator-targeting moiety conjugates using known chemistry.
Chelator conjugates of the invention may be prepared by various methods depending upon the chelator chosen. The peptide portion of the conjugate if present is most conveniently prepared by techniques generally established in the art of peptide synthesis, such as the solid-phase approach. Solid-phase synthesis involves the stepwise addition of amino acid residues to a growing peptide chain that is linked to an insoluble support or matrix, such as polystyrene. The C-terminus residue of the peptide is first anchored to a commercially available support with its amino group protected with an N-protecting agent such as a t-butyloxycarbonyl group (tBoc) or a fluorenylmethoxycarbonyl (FMOC) group. The amino protecting group is removed with suitable deprotecting agents such as TFA in the case of tBOC or piperidine for FMOC and the next amino acid residue (in N-protected form) is added with a coupling agent such as dicyclocarboimide (DCC). Upon formation of a peptide bond, the reagents are washed from the support. After addition of the final residue, the peptide is cleaved from the support with a suitable reagent such as trifluoroacetic acid (TFA) or hydrogen fluoride (HF).
Conjugates may further incorporate a linking group component that serves to couple the peptide to the chelator while not adversely affecting either the targetting function of the peptide or the metal binding function of the chelator.
In accordance with one aspect of the invention, chelator conjugates incorporate a diagnostically useful metal capable of forming a complex. Suitable metals include radionuclides such as technetium and rhenium in their various forms such as99mTcO3+, 99mTcO2+, ReO3+ and ReO2+. Incorporation of the metal within the conjugate can be achieved by various methods common in the art of coordination chemistry. When the metal is technetium-99m, the following general procedure may be used to form a technetium complex. A peptide-chelator conjugate solution is formed initially by dissolving the conjugate in aqueous alcohol such as ethanol. The solution is then degassed to remove oxygen then thiol protecting groups are removed with a suitable reagent, for example with sodium hydroxide and then neutralized with an organic acid such as acetic acid (pH 6.0-6.5). In the labelling step, a stoichiometric excess of sodium pertechnetate, obtained from a molybdenum generator, is added to a solution of the conjugate with an amount of a reducing agent such as stannous chloride sufficient to reduce technetium and heated. The labelled conjugate may be separated from contaminants 99mTcO4xe2x88x92 and colloidal 99mTcO2 chromatographically, for example with a C-18 Sep Pak cartridge.
In an alternative method, labelling can be accomplished by a transchelation reaction. The technetium source is a solution of technetium complexed with labile ligands facilitating ligand exchange with the selected chelator. Suitable ligands for transchelation include tartarate, citrate and heptagluconate. In this instance the preferred reducing reagent is sodium dithionite. It will be appreciated that the conjugate may be labelled using the techniques described above, or alternatively the chelator itself may be labelled and subsequently coupled to the peptide to form the conjugate; a process referred to as the xe2x80x9cprelabelled ligandxe2x80x9d method.
Another approach for labelling conjugates of the present invention involves techniques described in a co-pending U.S. application Ser. No. 08/152,680 filed Nov. 16, 1993, incorporated herein by reference. Briefly, the chelator conjugates are immobilized on a solid-phase support through a linkage that is cleaved upon metal chelation. This is achieved when the chelator is coupled to a functional group of the support by one of the complexing atoms. Preferably, a complexing sulfur atom is coupled to the support which is functionalized with a sulfur protecting group such as maleimide.
When labelled with a diagnostically useful metal, chelator conjugates of the present invention can be used to detect sites of inflammation by procedures established in the art of diagnostic imaging. A conjugate labelled with a radionuclide metal such as technetium-99m may be administered to a mammal by intravenous injection in a pharmaceutically acceptable solution such as isotonic saline. The amount of labelled conjugate appropriate for administration is dependent upon the distribution profile of the chosen conjugate in the sense that a rapidly cleared conjugate may be administered in higher doses than one that clears less rapidly. Unit doses acceptable for imaging inflammation are in the range of about 5-40 mCi for a 70 kg individual. In vivo distribution and localization is tracked by standard scintigraphic techniques at an appropriate time subsequent to administration; typically between 30 minutes and 180 minutes depending upon the rate of accumulation at the target site with respect to the rate of clearance at non-target tissue.